Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$172.25	10.816%	$190.8806	$190.88	$190.90	$190.90
Purchase #2	$215.76	8.174%	$233.3962	$233.40	$233.40	$233.40
Purchase #3	$217.61	7.261%	$233.4107	$233.41	$233.40	$233.40
Purchase #4	$21.53	13.544%	$24.446	$24.45	$24.45	$24.40
Purchase #5	$78.27	8.389%	$84.8361	$84.84	$84.85	$84.80
Purchase #6	$64.38	4.162%	$67.0595	$67.06	$67.05	$67.10
Purchase #7	$44.79	3.573%	$46.3903	$46.39	$46.40	$46.40
7 purchase totals =	$814.59		$880.4194	$880.43	$880.45	$880.40